I like the looks of all of them but I'm still going to take my time writing about what could have been done better in all of them:
1. The look is void of any life. Or rather, it looks like an afterlife kind of setting you used, so try pumping some colors into the mix (be sure to blend them well!) like blue or yellow on the midtones.
2. The contrast and colors look great, but either remove that vignette or get yourself a good vignette with Magic Bullet Looks rather than the light ray effect looking vignette.
Much more freedom in your settings and you can most likely achieve any effect you desire to create.
3. Seeing you tried to create something similar to Megaton's CC I assume you tried going for a post-apocalyptic look.
You've got the colors completely perfect but try to adjust the brightness settings a bit - the sky's so bright it almost hurts my eyes, but the rest is perfect.
4. Not sure if I can say anything critical about this. I like the colors and use of bloom, nothing to complain about for me in this one.
Fuck around with effects even more and you'll create some of the best CCs known to GTAS. Keep it up, you've got skill.